This tab is the main lock-in amplifier control panel for HF2LI
Instruments with the HF2-MF Multi-frequency option installed. Users with
instruments without this option installed are kindly referred to
The Lock-in tab is the main control center of the instrument and open
after start up by default. Whenever the tab is closed or an additional
one of the same type is needed, clicking the following icon will open a
new instance of the tab.
Table 1: App icon and short description
Quick overview and access to all the settings and properties for signal generation and demodulation.
The default view of the Lock-in tab is the parameter table view. It is
accessible under the side tab labeled All and provides controls for all
demodulators in the instrument. Moreover, for each individual
demodulator there is a functional block diagram available. It is
accessible under the side tab labeled with the corresponding demodulator
The Signal Inputs section allows the user to define all relevant
settings specific to the signal entered as for example input coupling,
range, etc. Some of the available options like phase adjustment and the
trigger functionality are collapsed by default. It takes one mouse click
on the "+" icon in order to expand those controls. On the right-hand
side of the Lock-in tab the Signal Outputs section allows to define
signal amplitudes, offsets and range values.
The Scaling field below the Range field can be used to multiply the
Signal Input data for instance to account for the gain of an external
amplifier. In case there is a transimpedance gain of 10 V/A applied to
the input signal externally, then the Scaling field can be set to 0.1
and the Units field can be set to A in order to show the actual current
readings through the entire user interface.
There are two buttons below the Scaling field that can be toggled: the
AC/DC button and the 50 Ω/ 1 MΩ . The AC/DC button sets the coupling
type: AC coupling has a high-pass cutoff frequency that can be used
to block large DC signal components to prevent input signal saturation
during amplification. The 50 Ω/ 1 MΩ button toggles the input
impedance between low (50 Ω) and high (approx. 1 MΩ )
input impedance. With 50 Ω input impedance, one will expect a reduction
of a factor of 2 in the measured signal if the signal source also has an
output impedance of 50 Ω.
The Oscillator section indicates the . Where the Mode indicator
shows Manual the user can define the oscillator frequency manually
defined by typing a frequency value in the field. In case the oscillator
is referenced to an external source the Mode indicator will show ExtRef
and the frequency field is set to read-only. External reference requires
a PLL to do the frequency mapping onto an internal oscillator.
Successful locking is indicated by a green light right next to the
The next section contains the Demodulators settings. The block
diagram displayed in Figure 2
indicates the main demodulator components and their interconnection. The
understanding of the wiring is essential for successfully operating the
In the Input Signal column one defines the signal that is taken as input
for the demodulator. A wide choice of signals can be selected: Signal
Inputs, the Trigger Inputs, the Auxiliary Inputs and Auxiliary Outputs.
This allows to use the instrument for many different measurement
For each demodulator an additional phase shift can be introduced to the
associated oscillator by entering the phase offset in the Phase column.
This phase is added both, to the reference channel and the output of the
demodulator. Hence, when the frequency is generated and detected using
the same demodulator, signal phase and reference phase change by the
same amount and no change will be visible in the demodulation result.
Demodulation of frequencies that are integer multiples of any of the
oscillator frequencies is achieved by entering the desired factor in the
Harm column. The demodulator readout can be obtained using the Numeric
tab which is described in
In the middle of the Lock-in tab is the Low-Pass Filters section where
the filter order can be selected in the drop down list for each
demodulator and the filter bandwidth (BW 3dB) can chosen by typing a
numerical value. Alternatively the time constant of the filter (TC) or
the noise equivalent power filter bandwidth (BW NEP) can be chosen by
clicking on the column’s header. For example, setting the filter order
to 4 corresponds to a roll off of 24 dB/oct or 80 dB/dec i.e. an
attenuation of 104 for a tenfold frequency increase. If the
Low-Pass Filter bandwidth is comparable to or larger than the
demodulation frequency, the demodulator output may contain frequency
components at the frequency of demodulation and its higher harmonics. In
this case, the additional Sinc Filter can be enabled. It attenuates
those unwanted harmonic components in the demodulator output. The Sinc
Filter is also useful when measuring at low frequencies, since it allows
to apply a Low-Pass Filter bandwidth closer to the demodulation
frequency, thus speeding up the measurement time.
The data transfer of demodulator outputs is activated by the En button
in the Data Transfer section where also the sampling rate (Rate) for
each demodulator can be defined.
The Trigger section next to the Data Transfer allows for setting trigger
conditions in order to control and initiate data transfer from the
Instrument to the host PC by the application of logic signals (e.g. TTL)
to either Trigger Input on the back panel.
The block diagram view of the main instrument functions is also
sometimes called the "Graphical Lock-in Tab". Depending on how many
demodulators are available in the instrument a set of numbered side tabs
are available giving access to a Graphical Lock-in Tab for each
demodulator. The block diagrams are fully functional and provide the
user with a visual feedback of what is going on inside the instrument.
All control elements that are available in the Parameter Table detailed
in the previous section are also present in the graphical
The block diagram in Figure 3 describes
the signal path throughout the instrument for the case when the internal
oscillator is used as reference. The Signal Inputs and
Reference/Internal Frequency are described on the left side, the core of
demodulation with the mixer and low-pass filter is located in the center
of the tab and the Signal Outputs, the Auxiliary Outputs as well as the
data transfer to the PC is sketched on the right.
The block diagram in Figure 4 describes
the signal path throughout the instrument for the case when an external
reference is used. This setting is only available for demodulator 7/8.
In order to map an external frequency to any of the oscillators, go to
the Reference section of demodulator 7/8 and change the mode to ExtRef.
This demodulator will then be used as a phase detector within the
phase-locked loop. The software will choose the appropriate filter
settings according to the frequency and properties of the reference
signal. Once a demodulator is used to map an external frequency on to
one of the internal oscillators, it is no longer available for other
Defines the gain of the analog input amplifier. The range should exceed the incoming signal by roughly a factor two including a potential DC offset.
The instrument selects the next higher available range relative to a value inserted by the user. A suitable choice of this setting optimizes the accuracy and signal-to-noise ratio by ensuring that the full dynamic range of the input ADC is used.
ON / OFF
Enable Signal Input.
Automatic adjustment of the Range to about two times the maximum signal input amplitude measured over about 100 ms.
Applies an arbitrary scale factor to the input signal.
Defines the physical unit of the input signal. Use *, / and ^ operators, e.g., m or m/s^2.
The value in this field modifies the readout of all measurement tools in the user interface. Typical uses of this field is to make measurements in the unit before the sensor/transducer, e.g. to take an transimpedance amplifier into account and to directly read results in Ampere instead of Volts.
OFF: DC coupling
Defines the input coupling for the Signal Inputs. AC coupling inserts a high-pass filter.
ON: AC coupling
OFF: 1 MΩ
Switches between 50 Ω (ON) and 1 MΩ (OFF).
ON: 50 Ω
ON: Differential voltage input
Switches between single ended (OFF) and differential (ON) measurements.
OFF: Single ended voltage input
Indicates how the frequency of the corresponding oscillator is controlled (manual, external reference, PLL, PID). Read only flag.
The user setting defines the oscillator frequency.
An external reference is mapped onto the oscillator frequency.
The HF2-PLL option controls the oscillator frequency.
The HF2-PID option controls the oscillator frequency.
0 to 50 MHz
Frequency control for each oscillator.
ON / OFF
Oscillator locked to external reference when turned on.
Select the reference mode (manual or external reference) or indicate the unit that uses the demodulator (e.g. PLL).
Default lock-in operating mode with manually set reference frequency.
The demodulator is used for external reference mode and tracks the frequency of the selected reference input. The demodulator bandwidth is set automatically to adapt to the signal properties.
The demodulator is used by the HF2-MOD option, e.g. for the direct demodulation of carrier and sideband signals.
Connects the selected oscillator with the demodulator corresponding to this line. Number of available oscillators depends on the installed options.
1 to 1023
Multiplies the demodulator's reference frequency with the integer factor defined by this field.
If the demodulator is used as a phase detector in external reference mode (PLL), the effect is that the internal oscillator locks to the external frequency divided by the integer factor.
Demod Freq (Hz)
0 to 50 MHz
Indicates the frequency used for demodulation and for output generation.
The demodulation frequency is calculated with oscillator frequency times the harmonic factor. When the HF2LI-MOD option is used linear combinations of oscillator frequencies including the harmonic factors define the demodulation frequencies.
-180° to 180°
Phase shift applied to the reference input of the demodulator.
When the HF2LI-MF option is used, the phase shift is also applied to the Signal Outputs.
Adjust the phase of the demodulator reference automatically in order to read zero degrees at the demodulator output.
This action maximizes the X output, zeros the Y output, zeros the Θ output, and leaves the R output unchanged.
Selects the signal source to be associated to the demodulator.
Sig In 1
Signal Input 1 is connected to the corresponding demodulator.
Sig In 2
Signal Input 2 is connected to the corresponding demodulator.
Aux In 1
Auxiliary Input 1 is connected to the corresponding demodulator. This input is only available on demodulators 7 and 8 used for the External Reference mode. The input bandwidth is limited to 20 kHz.
Aux In 2
Auxiliary Input 2 is connected to the corresponding demodulator. This input is only available on demodulators 7 and 8 used for the External Reference mode. The input bandwidth is limited to 20 kHz.
DIO D0 is connected to the corresponding demodulator. This input is only available on demodulators 7 and 8 used for the External Reference mode. The input bandwidth is limited to 2 MHz.
DIO D1 is connected to the corresponding demodulator. This input is only available on demodulators 7 and 8 used for the External Reference mode. The input bandwidth is limited to 2 MHz.
Selects the filter roll off between 6 dB/oct and 48 dB/oct.
1st order filter 6 dB/oct
2nd order filter 12 dB/oct
3rd order filter 18 dB/oct
4th order filter 24 dB/oct
5th order filter 30 dB/oct
6th order filter 36 dB/oct
7th order filter 42 dB/oct
8th order filter 48 dB/oct
Defines the display unit of the low-pass filters: time constant (TC) in seconds, noise equivalent power bandwidth (BW NEP) in Hz, 3 dB bandwidth (BW 3 dB) in Hz.
Defines the low-pass filter characteristic using time constant (s) of the filter.
Defines the low-pass filter characteristic using the noise equivalent power bandwidth (Hz) of the filter.
BW 3 dB
Defines the low-pass filter characteristic using the 3 dB cut-off frequency (Hz) of the filter.
Defines the low-pass filter characteristic in the unit defined above.
ON / OFF
Enables the sinc filter.
When the filter bandwidth is comparable to or larger than the demodulation frequency, the demodulator output may contain frequency components at the frequency of demodulation and its higher harmonics. The sinc is an additional filter that attenuates these unwanted components in the demodulator output.
Makes all demodulator filter settings equal (order, time constant, bandwidth).
Enabling the lock copies the settings from demodulator 1 to all other demodulators. With locked filters, any modification to a filter setting is applied to all other filters, too. Releasing the lock does not change any setting.
ON / OFF
Enables the data acquisition and streaming of demodulated samples to the host computer for the corresponding demodulator. The streaming rate is defined in the field on the right hand side. Enabling a stream activates a corresponding element in the numeric tab and allows for demodulated samples to be visualized and analyzed in any of the LabOne measurement tools. Note: increasing number of active demodulators increases load on physical connection to the host computer.
0.22 Sa/s to 410 kSa/s
Defines the demodulator sampling rate, the number of samples that are sent to the host computer per second. A rate of about 7-10 higher as compared to the filter bandwidth usually provides sufficient aliasing suppression.
This is also the rate of data received by LabOne Data Server and saved to the computer hard disk. This setting has no impact on the sample rate on the auxiliary outputs connectors. Note: the value inserted by the user may be approximated to the nearest value supported by the instrument.
Demodulator Sampling Rate Lock
Makes all demodulator sampling rates equal.
Enabling the lock copies the settings from demodulator 1 to all other demodulators. With locked sampling rates, any modification to a sampling rate is applied to all other sampling rate fields, too. Releasing the lock does not change any setting.
Selects the acquisition mode of demodulated samples. Continuous trigger means data are streamed to the host computer at the Rate indicated.
Selects continuous data acquisition mode. The demodulated samples are streamed to the host computer at the Rate indicated on the left hand side. In continuous mode the numerical and plotter tools are continuously receiving and display new values.
Samples are sent to the host computer depending on DIO 0 triggering.
Samples are sent to the host computer depending on DIO 1 triggering.
Samples are sent to the host computer depending on DIO 0 and 1 triggering.
Defines the edge or level trigger mode for the selected Trigger input. Note: this field only appears when a non-continuous trigger is selected in the Trigger field.
Selects triggered sample acquisition mode on rising edge of the selected Trigger input.
Selects triggered sample acquisition mode on falling edge of the selected Trigger input.
Selects triggered sample acquisition mode on both edges of the selected Trigger input.
Selects continuous sample acquisition mode on high level of the selected Trigger input. In this selection, the sample rate field determines the frequency in which demodulated samples are sent to the host computer.
Selects continuous sample acquisition mode on low level of the selected Trigger input. In this selection, the sample rate field determines the frequency in which demodulated samples are sent to the host computer.
Select the unit of the displayed amplitude value.
ON / OFF
Enables individual output signal amplitude.
When the HF2LI-MF option is used, it is possible to generate signals being the linear combination of the available demodulator frequencies.
-range to range
Defines the output amplitude for each demodulator frequency as rms or peak-to-peak value.
A negative amplitude value is equivalent to a phase change of 180 degree. Linear combination of multiple amplitude settings on the same output are clipped to the range setting. Note: the value inserted by the user may be approximated to the nearest value supported by the Instrument.
ON / OFF
Main switch for the Signal Output corresponding to the blue LED indicator on the instrument front panel.
Defines the maximum output voltage that is generated by the corresponding Signal Output. This includes the potential multiple Signal Amplitudes and Offsets summed up. Select the smallest range possible to optimize signal quality.
This setting ensures that no levels or peaks above the setting are generated, and therefore it limits the values that can be entered as output amplitudes. Therefore selected output amplitudes are clipped to the defined range and the clipping indicator turns on. If 50 Ω target source or differential output is enabled the possible maximal output range will be half.
Selects output range ±10 mV.
Selects output range ±100 mV.
Selects output range ±1 V.
Selects output range ±10 V.
-range to range
Defines the DC voltage that is added to the dynamic part of the output signal.
ON / OFF
The signal supplied to the add input is added to the signal output.